The demand for wireless broadband data in cellular networks is expected to persistently increase. To meet this demand, a new study item entitled “Study on Licensed Assisted Access using LTE” was approved by the Third Generation Partnership Project (3GPP) in the Radio Access Network (RAN) meeting #65 to utilize the unlicensed spectrum using Long Term Evolution (LTE)-Advanced (LTE-A) technology. The idea behind Licensed Assist Access (LAA) is to extend the LTE technology into unlicensed spectrum deployments, thus enabling operators and vendors to leverage existing or planned investments in LTE/EPC (evolved packet core) hardware in the radio and core network, while coexisting with other technologies and fulfilling the regulatory requirements.
The study focuses on LTE Carrier Aggregation configurations and architecture where one or more low power Secondary cell(s) (Scell(s)) (e.g., based on regulatory power limits) operates in an unlicensed spectrum and is either DL (downlink)-only (e.g., supplemental DL) or contains UL (uplink) and DL, where the PCell (Primary cell) operates in licensed spectrum with either LTE FDD (frequency division duplexing) or LTE TDD (time division duplexing) technology.
LTE employs a hybrid automatic-repeat-request (HARQ) protocol on physical layers to handle transmission errors. HARQ-ACK (acknowledgement) for a transport block (TB) or SPS release PDCCH (physical downlink control channel)/EPDCCH (enhanced PDCCH) with a given DCI (downlink control information) format for a serving cell has three states, namely, ACK (Acknowledgement), NACK (Negative Acknowledgement) and DTX (Discontinuous Transmission). The receiver uses an error-detection code, typically a Cyclic Redundancy Check (CRC), to detect if the received packet is in error or not. If no error is detected in the received data packet, the received data is declared error-free and the transmitter is notified by sending a positive acknowledgement (ACK). On the other hand, if an error is detected, the receiver notifies the transmitter via a feedback channel by sending a negative acknowledgement (NACK). “DTX” occurs when the UE (user equipment) misses the PDCCH and does not detect any PDSCH (physical downlink shared channel) scheduled by the eNB, for example, due to deep channel fade, a strong interference, etc.